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Review Question - QID 106684

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QID 106684 (Type "106684" in App Search)
A 5 year-old-boy with a history of severe allergies and recurrent sinusitis presents with foul-smelling, fatty diarrhea. He is at the 50th percentile for height and weight. The boy's mother reports that he has had several such episodes of diarrhea over the years. He does not have any known history of fungal infections or severe viral infections. Which of the following is the most likely underlying cause of this boy's presentation?

Thymic aplasia

0%

1/245

Hyper IgE syndrome

11%

28/245

Severe combined immune deficiency

5%

12/245

Wiskott-Aldrich Syndrome

2%

4/245

IgA deficiency

79%

193/245

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This patient has history of recurrent infections of mucosal surfaces and presents with a likely Giardial infection, consistent with IgA deficiency.

Giardia lamblia is a protozoal organism that can cause diarrhea. Giardia causes diarrhea through non-invasive means. It attaches to the the lining of the duodenum and can thereby lead to malabsorption and fatty, foul-smelling diarrhea, often associated with severe bloating and flatulence. Transmission is via the fecal-oral route, frequently involving contaminated water. Giardial diarrhea is classically associated with campers. However, recurrent giardial infection is often associated with deficiency of IgA immunoglobin.

Cooper et al. discuss IgA deficiency. IgA deficiency is the most common primary immunodeficiency but may often go undiagnosed because symptoms may be mild. The most frequent symptom is recurrent infection of mucosal surfaces, including sinusitis and gastrointestinal infections. Patients with IgA deficiency are at an increased risk of autoimmune diseases. Patients with IgA deficiency have normal responses to injectable vaccinations.

Cerutti et al. discuss the role of IgA in preventing infection. IgA is the most abundant immunoglobin and is designed to protect mucosal surfaces. IgA dimers interact with an Ig receptor on the basolateral surface of epithelial cells and are translocated across to the luminal surface. IgA can serve to neutralize toxins, bacteria, and pro-inflammatory molecules as well as prevent microorganisms from adhering to mucosal surfaces. It is through this last mechanism that IgA prevents Giardial infection and proliferation.

Illustration A depicts a scanning electron micrograph of the intestines of a gerbil with numerous giardial organisms adherent to the mucosal surface.

Incorrect Answers:
Answer 1: Thymic aplasia often presents with hypocalcemia and recurrent viral or fungal infections.
Answer 2: Hyper IgE syndrome frequently presents at an early age with facial abnormalities, abscesses, and eczema.
Answer 3: Severe combined immune deficiency has severe recurrent viral, bacterial, fungal, and protozoal infections and failure to thrive.
Answer 4: Wiskott-Aldrich is characterized by the triad of thrombocytopenic purpura, infections, and eczema.

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